The Full Form of SQUID is Superconducting quantum interference device.

A SQUID (for superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely subtle magnetic fields, based on superconducting loops containing Josephson junctions.

SQUIDs are sensitive enough to measure fields as low as 5 aT (5×10⁻¹⁸ T) with a few days of averaged measurements. Their noise levels are as low as 3 fT·Hz^−½. For comparison, a typical refrigerator magnet produces 0.01 tesla (10⁻² T), and some processes in animals produce very small magnetic fields between 10⁻⁹ T and 10⁻⁶ T. Recently invented SERF atomic magnetometers are potentially more sensitive and do not require cryogenic refrigeration but are orders of magnitude larger in size (~1 cm³) and must be operated in a near-zero magnetic field.